Today's integrated circuits include a vast number of transistor, capacitor, resistor, or other semiconductor devices formed in a semiconductor. Smaller devices are the key to enhance performance and to increase reliability in devices. As devices are scaled down, however, the technology becomes more complex and new methods are needed to maintain the expected performance enhancement from one generation of devices to the next. This relates mainly toward the primary semiconducting material of microelectronics, namely Silicon (Si), or more broadly, to Si based materials. One of the most important indicators of device performance is the carrier mobility. There is great difficulty in keeping carrier mobility high in devices of the deep submicron generations. A promising avenue toward better carrier mobility is to modify slightly the semiconductor that serves as raw material for device fabrication. It has been known, and recently further studied that Si, strained in tension, has intriguing carrier properties. Mechanical stress in the channel region markedly influences the performance and reliability of MOS devices. (See for example, Ito et al, “Mechanical stress effect of etch-stop nitride and its impact on deep submicron transistor design,” NEC Corporation, IEDM 2000, San Francisco, Calif.). It has been known that a nitride etch stop film causes tensile stress in the Si substrate. Thus, there has been a lot of interest in high-stress nitride etch stop film in the fabrication of MOS devices.
Tensile stress may be obtained by forming a nitride etch stop to create stress (that translates to strain in the underlying silicon) in the channel of a MOS device. Device mobility has been extensively studied by introducing strain in the channel. One such technique is the use of contact etch stop nitride layer as a stressor. To achieve increased drive current via increased carrier mobility and velocity, thicker nitride layers may be used to meet higher, specified stress levels.